so that was sort of quite shaking to me. i thought this must be a statistical fluke. it was not quite significant. this would surely go away when we had more data. narrator: so paabo told his team to do the work again... and again... and again. we really needed to make it absolutely sure that we were right. we started to look at the problem from different angles. and every time we would ask the question in a little bit different way. the answer would come back it's neanderthal. we were able to convince one another and eventually the world that we have a little bit of neanderthal ancestry in modern human genomes.

narrator: the amount of neanderthal dna in these modern genomes is small, between just one and four percent but the implications are staggering. after migrating out of africa, early humans must have mated with neanderthals and produced fertile offspring who inherited segments of neanderthal dna. what we have shown clearly is that we could interbreed with them, we could have fertile children and at least some of these children became incorporated in the human community and reproduced and contributed to present-day humans. narrator: paabo's groundbreaking research forces a radical shift in perspective regarding neanderthals. they were genetically close enough to have children with our species. they probably also had language. and there are yet more revelations as archaeologists reexamine previously

discounted evidence in favor of neanderthal skills and abilities. a hallmark of our species is our age-old affinity for art ritual and adornment. stringer: we see the astonishing cave art. we see statuettes over the whole range of modern humans from western europe right across to siberia. and i think that's part of the fact that modern humans are entering new territories they're covering wider distances and they're having to signal and network with each other. narrator: communicating with others through art and ritual has long been considered a uniquely human trait. joao zilhao: there has been the notion that neanderthals were less intelligent

and one way archaeologists have to deal with this question is by assessing the extent to which people used symbols. narrator: evidence of neanderthal symbolism has been elusive until recently. this is one of many fragments of manganese dioxide a black mineral found in a neanderthal cave in france its tip worn down as if used as a crayon. in neanderthal sites in gibraltar archaeologists have discovered cut marks on the wing bones of crows and birds of prey bones with little value as food. the marks suggest neanderthals were cutting off the feathers and using them to decorate their hair or bodies.

and in spain, seashells have revealed faint traces of hematite, or iron ore, a red mineral often used as pigment. neatly pierced holes allow the decorated shells to be worn as ornaments. anthropologist joao zilhao believes the evidence offers a glimpse into the neanderthal mind. now, he is reexamining finds from a neanderthal site in spain excavated in the '80s. zilhao: this is a fragment of a naturally pointed horse bone and when we looked at the tip of the bone under the microscope we found that there was lots of reddish dots.

narrator: although so faded they are hard to see the chemical analysis proves the spots are the red pigment hematite. and there is more. zilhao: this shell is from the mediterranean oyster and you can see adhering to the inner side of the shell a remnant of a pigment which is black and reflective. narrator: zilhao has found a pencil-like sliver of bone with a red mineral at its tip, and a shell stained with a shiny pigment alongside other fragments of colored minerals. it adds up to a significant collection, or so zilhao believes.

you know, they look like just shells collected off the beach but the amount of information they contain is tremendous. narrator: putting all the pieces of the puzzle together zilhao is convinced he is looking at the remains of a neanderthal body-painting kit. zilhao: this suggests that what was being prepared in this shell was a cosmetic preparation used as a tool to prepare something like glitter makeup. this is the smoking gun. we have here the case to settle the controversy concerning neanderthal symbolism. narrator: zilhao believes neanderthals used body paint

as a symbolic way of distinguishing friend from foe just as we do today. (chanting) zilhao: when you go to a football stadium and there are two teams playing, how do you know whether you're safe to sit next to someone who may be supporting the team that hates yours? you use an artifact that identifies you as a supporter. and it's this kind of information about yourself that these kinds of objects transmit. narrator: but even if the neanderthals were painting themselves and engaging in symbolic behavior, does it mean they thought the same way as modern humans? our modern human ancestors practiced ritual and religion. similar evidence for neanderthals

has been elusive. then a team of archaeologists made an intriguing discovery in southern spain. their finds hint at the existence of a neanderthal ritual. inside this cave, a team led by michael walker excavated a deep shaft in which they found more than 300 bones from around ten neanderthals buried by rockfalls from the unstable ceiling. three of the neanderthals stood out. walker thinks they weren't necessarily the victims of a rockfall. if there are rocks falling on you from a natural rockfall, it would be very strange to find nobody trying to escape and one of them with the hands close to the head

in almost sleeping position. narrator: although the bones of this young female are fused to the limestone rock and are hard to see, michael walker thinks her body may have been carefully arranged in a fetal position. if he's right, this was no rockfall. around 50,000 years ago, someone had intentionally buried her piling stones to protect her body. and this cave had yet more to reveal. near the girl's body walker's team uncovered the fossilized bones of a pair of panther paws. walker: this articulated paw of a panther was found close by. and since the panther hadn't eaten and disturbed the bones here it's more likely that the neanderthals disturbed the panther and cut its paw off. i just wonder whether in the way

that today hunters in america cut off bear paws, i'm wondering if the neanderthals occasionally didn't cut off a panther paw and keep it as a trophy. narrator: walker's idea-- that the severed panther paws were a trophy or funeral offering-- is an intriguing speculation. i think that there are enough examples of neanderthal burials, well articulated individuals to suggest that they are intentionally burying their dead. perhaps when you come to the issue of grave goods and whether they're putting material in those graves and whether they're, if you like, sending messages beyond the grave through these materials, that's more controversial.

you see in humans elaborate ritual burials maybe about 27,000 years ago the clearest evidence in this place in russia. these two children are buried with, like, 10,000 beads. there's nothing like that in neanderthal burials. narrator: whether neanderthal burials are evidence of complex rituals and beliefs is hotly debated. but many clues now point to the idea that neanderthals were more accomplished and advanced than previously thought. and this opens up perhaps the biggest question of all: why are we still here and neanderthals are not?

the neanderthal story seems simple. their forerunners reached europe around 800,000 years ago. when homo sapiens joined them around 40,000 years ago, it marks the beginning of the end. some 10,000 years after modern humans arrive virtually all traces of neanderthals are gone. some scientists believe we drove them into extinction by outcompeting them for scarce resources maybe even by killing them. but the latest evidence points to another possibility. soon after svante paabo's team revealed that neanderthals and modern humans outside africa

had interbred, anthropologist john hawks reopened the case files. he wanted to know if this interbreeding had happened a little or a lot. hawks needed more than just the five modern human genomes that paabo had analyzed. and he got a lucky break. a team of scientists published a huge new database of individual human genomes from around the world. the 1000 genomes project data began to become available. and so we were able to expand the comparison to literally more than a thousand individuals from different populations. narrator: if interbreeding had been a relatively rare event, then all non-african humans across the world would have inherited the same small dosage of neanderthal dna.

but that's not what hawks found. hawks: now, my lab, we were able to look at more people in china, more people in tuscany in the uk. and as we're doing this, we're discovering that there are some differences among these populations. narrator: hawks uses the jelly beans to illustrate the relative percentages of neanderthal dna he found in different groups of modern humans across the world. we see that in china there is a little less. in europe it's a little more. and when we compare europeans, in southern europe, in tuscany it's a little more than it is in other parts of europe. narrator: outside africa, hawks' data showed the chinese have the smallest dose of neanderthal dna some individuals having as little as two percent.

but in tuscany, northern italy this rises to around four percent. so hawks' data shows that tuscans have more neanderthal genes than any other people living today. if hawks is right, ice age southern europe was a hotbed of neanderthal-human interbreeding. hawks: this was neanderthal habitat. modern humans were interbreeding with them, for a longer time and over a larger geographic space. and subsequently europeans got a little bit more neanderthal dna. narrator: today, a simple blood test can estimate how much of our genetic identity is neanderthal. hawks: do you guys want to find out? students: yes. are you sure you're ready? yes, yes, get over it, okay, all right. at 1.3 percent the least is arial. that's very characteristic actually of african americans in our sample.

next, 2.5 percent, is vang. and the most... you're left. how much do you think it is? no more than three percent. not five? i hope not. (everyone laughing) all right, you're the most with three percent, yes. narrator: this field of research is in its infancy and evolving rapidly. other experts report different percentages of neanderthal dna. but most agree on one key finding. there wasn't just a handful of sexual encounters between humans and neanderthals, but many. that presents a dramatically different picture of how humans and neanderthals interacted in ice age europe

and leads to a new outlook on the neanderthals' disappearance. hawks: when we think about the process of extinction in other kinds of animals, we think of it usually as a really sudden event like an asteroid hits the earth and they're gone. with the neanderthals, what you're looking at is a much more gradual process a process that unfolded over thousands of years. narrator: hawks believes the neanderthals' dna was absorbed by the dominant population. outnumbered ten to one by modern humans neanderthals weren't hunted to extinction by a supposedly superior species. they were bred out genetically swamped.

hawks: so a million, you know compared to three billion base pairs in your whole genome... i would frame the end of the neanderthals as a process of interaction and absorption. neanderthals were sort of on the losing end of that. and their only route toward success was probably interbreeding with our population. narrator: but is our dosage of neanderthal dna just a quirk of genetic history? or is there a serious side to this inheritance? what, if anything, have neanderthals done for us? ed green and his team are looking closer at the sections of neanderthal dna that we inherited. one obvious follow-up question is, what is the impact of neanderthal genetic contribution

into people today? narrator: most of the genes they examine don't have any known function. but then the team finds something intriguing: neanderthal dna in locations fundamental to our immune system involving genes that are vital to our ability to fight off disease. these areas are called human leukocyte antigens, or hlas. they make the cells that attack viruses and bacteria. since neanderthals lived in ice age europe for hundreds of thousands of years, their immune systems must have been specially adapted to fight off the diseases there. this was something that modern humans, arriving from africa didn't have.

our ancestors, when they came into the neanderthal range were, for the first time encountering this environment. our immune systems would not be adept at recognizing and fighting pathogens new to us. hawks: oh, it's absolutely a survival toolkit. hla types are important because they help our body resist disease. so it's very clear that one product of this interaction was the inheritance of immune system versions of genes. maybe they conferred some selective advantage. maybe the neanderthals have a version of these immune system genes that were beneficial for the neanderthal and they were beneficial to human people who got these genes by interbreeding. narrator: this is the epstein-barr virus linked to both mononucleosis and a type of blood cancer. green's team found that an hla we inherited from neanderthals

could reduce the risk of contracting this deadly virus. but this may be just the tip of the iceberg. as we look more and more at the neanderthal genome and characterize what things are where, i think we're going to find more of these. narrator: it seems the neanderthals who mated with our human ancestors may have given their offspring a lifesaving legacy, a legacy that is potentially saving lives even to this day. the genetic and archaeological evidence is still unfolding. but already it is telling us something profound. the neanderthal story goes to the heart of who we are today.

we're finding out we owe a debt to a mysterious, long-vanished branch of the human family in ways we are only just beginning to discover. on nova's website, you can watch this and other nova programs. where do we draw the line between humans and neanderthals? how do scientists define a species? explore the debate online. and, just what is it that makes us human? watch video extras hear from experts, and explore interactives. find us at pbs.org/nova. follow us on facebook and twitter. next time... scientists race to uncover a 100,000-year-old mystery.

there was something about this lake that was dangerous. an ancient world of fantastic creatures. but why did so many die here? man: if you were there at the wrong time, something might kill you. with only weeks remaining, can the riddles be solved? "ice age death trap," next time on nova. major funding for no major funding for nova is provided by: supporting nova and promoting public understanding of science. and the corporation for public broadcasting, and by pbs viewers like you. this nova program is available on dvd. to order, visit shoppbs.org,

or call 1-800-play-pbs. nova is also available for download on itunes. captioned by media access group at wgbh access.wgbh.org available now on shoppbs downton still stands. i'm looking forward to all sorts of things. what?! no one must know! i'm warning you...

to order, visit shoppbs. also available on itunes. coyle: john bates. i read this character, and there was something... i was drawn to him as much by what he didn't say as by what he did. i thought what he concealed was as interesting as what he revealed a kind of stoicism-- something very old-fashioned but also something quite mysterious as well. there's an element of mystery there. it's all about survival. he survived not losing his job. he survived the return of his wife. and he's now surviving prison, so it's about survival for bates. there are moments of reprieve. falling in love with anna was unexpected. what i loved about that relationship was the sort of restraint. it developed over a long period of time.

it was a romance that blossomed through a sympatico. she empathized with him. she's a delightful person and a delightful actor. so, there's a tenderness there, a delicacy. there's a lot of restrictions for them. it was frowned upon to have relationships within the servant class and within the household. it wasn't encouraged at all, so you had those kind of restraints. it was a slow burn and people have really invested in that. so we've got a lot in the bank for the trouble that they subsequently meet. just little moments, very beautiful and we're still having them.